1. Field of the Invention
The present invention relates to a method for taking samples, making flow measurements, quantity gauging, and possibly performing other analyses in reservoir fluid run into within a ground formation, for example, when drilling an exploration well for hydrocarbons.
2. Prior Art
Use of new technology in, inter alia, drilling and production in ground formations exhibiting high pressure and temperature, injection of water and gas for increasing the degree of extraction, multiphase production on the seabed and transport of produced hydrocarbons in pipelines on the seabed, makes constantly ever greater demands on maximum knowledge about the physical and chemical properties of the gas, oil and water to be produced from the deposit. Previously, such knowledge about the reservoir fluid within the ground formation was normally provided by means of testing at complete production. However, today there is a clear tendency towards increased use of various sampling tools which, during drilling, are passed down into and pulled up from the well by means of a wire string. The last mentioned method, however, gives fewer possibilities to provide data about relevant parameters of the reservoir fluid than what is possible at full production testing.
Each of the above-mentioned methods has its different advantages and weaknesses. The strength of full production testing is that data can be collected in a large volume of the reservoir fluid, so that the data become very reliable. The main weakness is the large expenses incurred upon, for example, renting a rig and other necessary accessories. Another significant deficiency is that it becomes necessary with one or another form of handling of the large amount of reservoir fluid conducted up to the surface. Today, this takes normally place through undesirable burning of the oil and gas.
Important advantages of use of sampling and measuring accessories lowered down into the well by mans of a wire string, is that samples of the reservoir fluid can be taken continuously during the drilling, and that this can take place with far less expenses than upon full production testing. Nor is it necessary to burn oil and gas. The main weakness of the accessory is, as already mentioned, the limitations in what the accessory can provide of data about relevant parameters for the reservoir fluid. For example, absolutely necessary data about the flowing conditions in the reservoir fluid can not be provided. Nor is the accessory usable in connection with saturated gas reservoir as pressure and temperature can not be stabilized. The weakness is increased further due to the fact that very small amounts of the reservoir fluid are taken out, and that the accessory has to be handled from the surface. Moreover, the last mentioned condition may result in that the measuring results for the reservoir fluid become unreliable. Such errors in the measuring results may be due to, inter alia, the fact that the accessory is not brought into the correct position within the reservoir during the sampling; that the reservoir fluid where samples are taken is contaminated with drilling fluid supplied during the drilling, and that sand accompanying the reservoir fluid during the sampling causes leakage in the accessory.
The above-described problems are solved by the present method. The present method comprises sealing an area of the ground formation""s hydrocarbon carrying layer and supplying reservoir fluid from the hydrocarbon carrying layer into a pipe string. Sampling and/or flow measuring, quantity gauging, and possibly other analysis are carried out in the sealed area of the well while the reservoir fluid flows controllably into the pipe string. The reservoir fluid is then returned from the pipe string to the hydrocarbon carrying layer within the ground formation after completing the sampling and analysis.
A great advantage of the present method over prior methods is that the sampling, flow measurements, quantity gauging, or other analysis can be carried out in reservoir fluid positioned down within the hydrocarbon carrying layer. Such reservoir fluid is stabilized as much as possible and, moreover, free of drill fluid.
The supply of reservoir fluid may be controlled by means of a downhole valve or a surface valve. A piston separates the reservoir fluid from water or N2. Subsequent to perforation of the well, the piston moves upward when reservoir fluid is let in with a speed adjusted by means of the valve. Thus, the inflow of reservoir fluid can be measured by reading the amount of liquid (water or N2) which, during the inflow, has flowed into a tank at the surface. When the reservoir fluid has risen so high up in the string that the liquid has reached the security valve, often called the BOP, at the seabed or the surface, the piston is stopped by a seat. Then, all tests are carried out downhole, and the reservoir fluid is pressed back to the reservoir.
Uniform pressure data are achieved due to a stabilized inflow of reservoir fluid into the pipe string. The sampling, flow measurements, quantity gauging or other analyses may be performed with an accessory which is available at any time, so that as much data as possible about the reservoir fluid can be gathered. Trace elements, or tracers, may be added to the reservoir fluid in order to carry out flow measurements, while still returning the reservoir fluid to the hydrocarbon carrying layer from which it was taken.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.